Process of maintaining a uniform current in electric circuits



(N0 M0del.) 4 Sheets-Sheet 1. J. M. BRADFORD. PRCCESSCI' MAINTAINING AUNIFORM CURRENT IN ELECTRIC CIRCUITS.

No. 429,333. PatentedJune 3,1890.

R 0 T N E V N W ITN ES SE82 QM'WW. NMM.,

(No Model) 4 Sheets-Sheet 2.

J. M. BRADFORD. PROCESS OF MAINTAINING A UNIFORM CURRENT IN ELECTRICCIRCUITS.

Patented June 3,1890

WITNESSES: INVEN OR:

5 W\.\3va.-MW

4 Sheets-Sheet 3x (No Model.)

J. M. BRADFORD. v PROCESS OF MAINTAINING A UNIFORM CURRENT IN ELECTRICCIRCUITS.

Patented June 3, 1890.

WITNESSES (No Model.) 4 Sheets-Sheet 4.

, J. M. BRADFORD. PROCESS OF MAINTAINING A UNIFORM CURRENT. IN ELECTRICGIRGUIT'S.

No. 429,333. Patented June 3, 1890.

q o o WITNESSES: INVENTOB'.

UNITED STATES PATENT OFFICE.

JULIEN M. BRADFORD, OF PORTLAND, MAINE.

PROCESS OF MAINTAINING A UNIFORM CURRENT IN IZLECTRIC CIRCUITS.

SPECIFICATION forming part of Letters Patent No. 429,333, dated June 3,1890.

' Application filed September 22, 1888. Serial No. 286,125, (No model.)

To all whom it may concern.-

Be it known that I, JULIEN M. BRADFORD, a citizen of the United States,residing at Portland, in the county of Cumberland and State of Maine,have invented new and useful Improvements in Processes of MaintainingUniform Current in Electric-Lighting Circuits, of which the following isa specification.

My invention relates to systems of electrical distribution; and thepurpose thereof is to provide automatic means whereby the currentstrength upon circuits may be regulated and maintained at a certaindegree or at a substantially uniform intensity.

The methods described in the following specification are widelyapplicable to different systems of generating and distributing directand alternating currents, being especially intended to control thecurrent on incandescent and arc light circuits, for the purpose ofpreventing dangerous electrical pressure, securing uniformity of light,and other advantages incident to proper regulation.

Automatic methods for the above purpose, heretofore described, arecharacterized by one or more of the following features: inability tomove the regulating mechanism with quickness and precision on thecommencement of a slight variation of the current to be regulated and tocontrol. or cut off said movement with accuracy when suflicientlyexpended; second, inability to maintain the regulating mechanism in agiven position unassisted by the force of the current to be regulated.It results, therefore, that automatic regulators based upon said methodsact very slowly if sensitive to slight changes in the current to beregulated and capable of moving the regulating mechanism with precisionthrough con siderable distances.

In the following specification will be described methods diti'eringradically from the foregoing, inasmuch as regulating action even ofgreat energy can be produced by the slightest change in the current tobe regulated, and this action can be controlled with as great accuracyas that formerly obtained from slowworking'methods. Therefore by suchamethod material changes in mainline currents can be anticipated orprevented, instead of being reduced after they are developed.

Prominent among the purposes for which this invention provides a method,one or more of which may be used in practice, are the following,described in six paragraphs, as follows:

First, a method whereby a rheostat or other the operation being suchthat the action obtained thereby may be the sum or the difference of theaction of two or more of said rheostats or factors acting at the sametime.

lhird, a method whereby progressive regulating action may be obtained,as before stated, for the purpose of actuating a rheostat or otherregulating factor controlling a circuit, and of holding stationary saidrheostat or factor unaided by the force of the current on said circuit.

Fourth, a method of operating regulating apparatus progressively, asbefore stated, and with a minimunrexpenditure of motive power to adaptthe apparatus for use in places remote from the dynamo-station, I

Fifth, a method whereby a current-indicator of such construction is usedthat regulating apparatus is actuated by successively closing localcircuits, thereby preventing oxidation of the contact-points andassuring other advantages explained in the fifth section of thefollowing specification.

Sixth, methods of controlling the generative capacity of dynamo-electricmachines; also, other methods of arranging compensating circuits and ofmaintaining the com pensation when secured.

\Vhile my invention may be carried out by any of the several systems andmodes of operation hereinbefore referred to, I do not herein claim saidsystems specifically, restricting myself in this application to claimsfor the general mode of operation, and the several systems are describedsimply to show that the method may be carried into effect in variousways.

Of the drawings illustrating this invention, Figure 1 is a front view ofa regulator with a current-indicator in electrical connection therewith.Fig. 2 is a front view of a regulating device and also wheel 16. Fig. 3is an end view of Fig. 1. Fig. 1 is a front view showing a diiferentmode of arranging magnets 15. Fig. 5 is a diagram showing theconstruction of a rheostat that may be operated by a regulator. Fig. 6is a front view of a regulator in electrical connection with acurrent-indicator. Fig. 7 is a front View of two eccentrics arranged foraccumulative and differential action. Fig. 8 is a plan of an arrangementfor concentrating regulating action. Fig. 9 is a diagram illustrating amethod of operating regulating apparatus with economy of motive power.Fig. 10 is a detail of 11. Fig. 11 is a frontview of acurrent-indicator. Figs. 12, 13, 11, and 15 are diagrams illustratingapplications of the regulating apparatus described in thisspecification.

In describing this invention and also modes of applying it to practicethe following specification will be divided into six sections, asfollows:

First. Regulator A, Fig. 1, should be placed in any suitable placerelatively to the work to be performed. The pulley 5 may be bolted toany suitable source of power, such as the power-shaft driving a dynamo.To pulley 5 is fixed shaft 2, which carries eccentrics 6, fixed on saidshaft at an angle one to the other, as shown in Fig. 7. The eccentrics 6operate regulating devices, one of which is shown in Fig. 2. This deviceconsists of a T-shaped lever 28, with open frame at 29, pawls 30,springs 31, and electro-magnets 15. The levers 28 are pivoted on shaft1, which has regulating-wheels 16 fixed to it. The regulating-wheelshave teeth, and a gap or space may be uncovered by teeth, if desired, asa means of limiting the movement of said wheels. Shaft 1 may move arheostat of the construction shown in Fig. 5 as a means of regulating acircuit, or said shaft may move the com imitator-brushes of adynamo-electric machine as a means for that purpose, several modes ofapplying the regulator being illustrated by Figs. 12, 113, 11, and 15,and explained in the sixth section of this specification. \Vhen therheostat is used as a means of regulating a current, it passes throughthe arrangement by way of the binding-posts 17 and 21, and consequentlyis of maximum force when the contact-arm 18 is at the extreme right, ofminimum force when the arm is at the extreme left, and of intermediateforce when the arm is in an intermediate position. The pawls 30 aredrawn away from the wheels 16 by springs 31; but should a magnet 15 beenergized a pawl 30 is drawn into engagement with a wheel 16 and causesit to move. Any suitable current-indicator may be electrically connectedwith this regulator, those capable of noting a gradual change in currentby a gradually-increasing deflection being preferred. In thecurrent-indicator C the helix. 1 3 receives through wires a fraction ofthe current from the circuit to be regulated, thereby causing lever 12to be moved or deflected more or less, according to changes of currentin said circuit. Above lever 1'3 is a binding-post 35, which derives alocal current of suitable strength from a dynamo or other source andcommunicates it to lever 12 by the wire connected thereto. Thebindingpost 36, representing the other pole of the local circuit, is inelectrical connection with magnets 15 of the regulator. The indicatorlever 12 is so adjusted that it will not touch either of the screws 15or 16, while the current to be regulated is of the right degree ofstrength; but should that current increase screw 15 is touched,completing a local circuit and energizing the left-hand magnet 15, whichcauses a pawl to engage with a wheel 16 and move shaft 1 to theleft,thereby red ucing the current, as subsequently explained in the sixthsection of this specification. The instant the current which is beingregulated is reduced to a normal degree of strength the lever 12 dropsfrom the screw 15, causing the local circuit to be broken and therebycausing magnet 15 to release pawl 30, which is instantaneously drawnaway from the teeth of a wheel 16 by a spring 31. This causes the shaft1 to stop on the instant of the disengagement of pawl 80 by reason ofthe friction of arm 18, which bears with slight pressure upon thecontaet-plates of the rheostat. The contact-spring 19 also bears withslight friction upon arm 18, in order to maintain an electricalconnection between them. The shaft 1 now remains at rest until thecurrent to be regulated declines below the normal degree, when screw 16is touched, causing a local circuit to be completed through theright-hand magnet 15, thereby causing a pawl 30 to move the shaft 1 tothe right and increase the current.

The regulator shown in Fig. 1 contains two regulating devices of theconstruction shown in Fig. 2; but three or more of said devices can withadvantage be arranged to work upon shaft 1, especially if it is desiredto increase quickness of action. Each regulating device should beoperated bya separate eccentric 6, arranged at an angle one to the otheron shaft 2. Increased quickness of action of such an arrangement resultsfrom the unequal circumferential velocity of the eccentric-disks 6. Suchbeingthe case, each during its moment of maximum movement will lead inmoving wheels 16 and shaft 1. 'lhereforcincreased regulating action canbe obtained by the arrangement without increasing the rate of motion ofthe driving-pulley 5. Instead of arranging a separate regulatirig-wheel16 to receive the action of each regulating device, as shown in Fig. 3,each wheel 16 may receive the action of two regulating devices byplacing the wheel between them, the pawls 30 being suitably arranged toengage with the wheel. Each magnet 15 is also capable of actuatingseveral pawls, so that the number of magnets is not necessarilyincreasedwhen more regulating devices are added.

The regulator last described differs from 4 others usedin the art by itscapacity for rapid progressive action combined with precision ofregulation, which commences on the inception of the slightest change inthe regulated current that can be detected by the currentindicator. Thisaction is under control. Its quickness is determined by the rate ofmotion of pulley 5 by the number of eccentrics and their angulararrangement, also by their diameter or throw, and said act-ion, whensufficiently expended, is instantaneously cut off. Pawls 30 are requiredto move but a slight distance to make engagement with a wheel 16.Therefore a com paratively weak current from the dynamo willsufliciently energize magnet 15 to cause a pawl to be thrown intoengagement. The pawls also bear against the teethof the wheels 16.Therefore the movement of said wheels is positive without slipping.Springs 31 apply sufficient tension near the pivot of pawls 30, so thatsaid pawls instan tan eously spring from wheels 16 on the breaking of alocal circuit. With such provisions there is hardly a possibility of thepawls acting at the same time on opposite sides of a wheel 1.6, andthereby straining or breaking some part of the regulator. Still if it isdesired to provide for such a contingency, an arrangement for thatpurpose is shown in Fig. 8 and described in the latter partot the secondsection of this specification.

The pawls of the regulator shown in Figs. 1 and 3 act with greatereffect and precision than pawl mechanism with the ordinary forward andreturn stroke. \Vhen pawls are operated in the latter manner, one-halfof the time is lost in making the return-strokes, which cause nomovement of the wheel which is being propelled. Therefore the action isintermittent instead of being continuous. Little is gained byincreasin gthe speed of the pawls, for at any rate of speed one-half of the strokesare ineffective, and excessive speed causes vibration and irregularityof action. It therefore results that ordinary pawl mechanism isincapable of either instantaneous or continuous action. By operatingpawls by eccentrics arranged on the driving-shaft at an angle, one tothe other, a new result is obtained. The pawls move in both directionsat the same time, the arrangement being thereby capacitated forinstantaneous, continuous, and accurate action in either direction. The

eccentrics may be said to be arranged for accumulative and differentialaction, because by this means action maybe accumulated in the samedirection 'or be applied first in one the pawl. Stationary magnets,however, have the advantage of each operating a considerable number ofpawls, as has been before explained.

Second. The regulator shown in Fig. 6 differs from that shown in Fig.],in having two separate shafts 4:, which, with the rheostats attached,are moved independently of each other by the regulating devices. Thecurrent to be regulated passes through both rheostats by way of thebinding-posts 17 and 21. The double rheostat, operated by two regulatingdevices and two eccentrics, changes the current passing through it withthe same quickness as a single rheostat operated by two regulatingdevices, (shown in Fig. 1;) but by increasing the number of regulatingdevices and eccentrics for operating the inde pendent shafts 4, or byseparately operating three or more rheostats in a series, thearrangement becomes capable of an in crease of action resulting from thecombined effect of two or more contact-arms 18, moving in the samedirection at the same time, or the difference of action of two or moreof said arms moving at once in opposite directions. Each regulatingdevice in the above regulator is the same as that shown in Fig. 2. Inpractice it probably will be preferred to use springs 31 of suilicienttension to cause a pawl 30 to disengage from a wheel I 16 on the instantof breaking a local circuit. If this tension is insutlicient to causethe pawls to disengage while they are in operative contact with wheels16, the stroke will continue for its entire length, but will beprevented from seriously disturbing the current which is being regulatedby the neutralizing effectof the other arm 18, which is caused to movein the opposite direction on the instant said current is slightlyovercompensated and the current-indicator c deflected thereby in theopposite direction. Fig. 8 shows another way of concentrating actionupon one shaft as for the purpose of moving the commutatorbrushes of adynamo-electric machine. The arrangement consists of a shaft 4, having agear D meshing with gears 48 on actuatingshafts 46 011 opposite sides ofgear D. The

shafts 4:9 carry the regulating wheels 16, which IIO the regulating;devices act oppositely at the same time the pinious l8 slip on theirshafts without imparting motion to the gear D. But, as before explained,springs 31 maybe of sufficient tension to cause pawls 30 to disengagefrom wheels 10 on the instant of breaking a local circuit, therebypreventing opposite ac tion at the same time. The springs 47 causesuflicicnt friction to overcome any slight momentu 111 of wheels 16.Therefore shaft l stops on the instant that the regulating devices ceaseto move it.

Third. By all the foregoing arrangements the regulating-wheels 16 movewith slight f riction, thereby causing the regulating mechanism attachedthereto to remain in any position to which it may be moved. An incipientvariation of the current which is being regulated is sufficient to causethe motive power to move contact-arm 1 8 or other regulating mechanism,and this mechanism is held by friction in the position to which it ismoved. Therefore a variation of force of the current which is beingregulated plays a secondary part in securin g a compensation of saidcurrent and no part in maintaining this compensation when secured. If agreat number of lamps are arranged in multiple are 011 a main line, itis evident that the current in amperes fed to the line should be smallwhen but few lamps are lighted, and that said current must be greatlyincreased when all the lamps are in use, although the electro-iuotiveforce of the line-current should at all times remain unchanged. On theother hand, if a certain number of lamps are arranged in series, thecurrent required is the same for a small as for a great number of lamps;but the electro-motive force must be increased if the number of lamps isincreased and decreased when the lamps are switched out of circuit inthe usual way, the regulation of the electro-motive force being for thepurpose of n'lainta-iniug a suitable electrical pressure to cause acurrent of a required nu mber of amperes to flow through the circuit.Besides the changes of resistance on the circuit, for which compensationmust be made, there are irregularities of the generative ca pacity ofthe dynamo from change in engine speed. It results, therefore, that itis often required to largely increase the current fed to a cireuit,whilcthe electro-motive force remains practically constant, and in othercases to increase the eleetro-motive force and maintain a constantcurrent.

The regulators described in this specification are adapted totransiently move the regulating mechanism for the purpose of preventingtransient irregularities of current, and also to sustain new adjustmentsof said mechanism unaided by the force of the current which is beingcontrolled. Therefore circuits may be regulated for constant potentialor for constant current.

Fourth. If it is desired to use the regulat in g apparatus in placesother than at the dy namo-station, said apparatus may in such instancesbe worked by a special motor, as ordinarily there will be no engine atwork in such places from which motive power can be derived. It will alsobe well to cause the motor to remain at rest, excepting while theregulating apparatus is being moved, as by this means power will beeconom ized tothe greatest extent. An arrangement for the above purposeis shown at Fig. 9, in which the elect-ricmotor J is attached to pulley5. A part of the current from the circuit to be regulated flows throughwires 25 to helix a3. It the current to be regulated increases beyondthe required degree, the indicator-lever 42 touches screw 45, causing alocal current to flow from binding-post to screw 45, thence through theleft-hand wire 3 to the left-hand magnets 15, thence through the coilsof motor J, and back to the other pole of the local circuit at 36. Themotor J starts the regulator by moving pulley 5, magnets 15 at the leftare energized, and a compensation is made in the current to beregulated, as before described. As soon as the compensation is completedthe indicator-lever l2 drops from screw 45, thereby breaking the localcircuit and stopping motor J. If the current to be regulated declinesbelow the right degree of i11- tensity, screw it) is touched, causingthe motor to start, the right-hand magnets 15 to be energized, thecurrent to be regulated, and the motor to again stop, when the indicatorlever it breaks the circuit through the righthand wire 3. It isprobable, unless motor I is of small power, requiring but a weak currentto operate it, that the contact-screws l5 and a0 would soon becomeoxidized by sparks escaping at the moment of breaking the local circuitsby lever l2. The liability to this dofeet and the necessity offrequently scraping and read justing the lever l2 and contactscrews toinsure the operation of the apparatus can be wholly avoided by causinglever 42 to successively close local circuits and thereby operate theapparatus, said method being fully explained in the next section of thisspecification. It is evident thatother motors-such as those worked bycompressed air, water, or by a weight-can be substituted for theelectric motor, as will also be nextexplained.

Fifth. A cu rrent-imlicator may successively close local circuits andthereby actuate regulatiug apparatus. Fig. 11 shows an instrument of theabove kind,which utilizes a slight power during its moments of action,to supply which pulleys 59, having friction-washers 60 attached to them,may be loosely supported upon shaft-s 62 and be belted to the powershaftof the dynamo; but where a power-shaft is inaccessible twowinding-drums, to which weights are attached, Fig. 10, may take theplace of pulleys 59 and frictionavashers (it). The friction-washers 60are attached to pulleys 59 and press with sufticient force upon gears 50to cause a wheel 1 to move when an armature-lever it is lifted, therebyallowing a fly t to pass. A fraction of the current from the circuittobe regulated flows through wires 25 to wire or other suitable conductor,thereby slightly heating it in proportion to the quantity of current.The needle 42, screws 53 and 57, contact-springs 55, :r, 00 m, and m areinsulated from the metallic bed-plate, upon which they are supported.The needle 42 is adjusted relatively to pin f and screws 53 and 57 insuch a manner that while the circuit to be regulated is carrying acurrent of normal strength needle 42 does not touch either screw 53 or57, but rests upon pin f. If that current increases, wire 50 expands,causing needle 42 to touch screw 53. If the current declines, wire 50contracts and screw 57 istouched. This current-indicator may besubstituted for indicator 0 of Figs. 1, 6, and 9, the wires 3 and 9 ofFig. 11 being for the purpose of conveying currents to magnets 15 of theregulating devices before described.

The operation is as follows: Ifscrew 53 is touched by needle 42, acurrent flows from battery 52 to needle 42, thence to screw 53,

thence through the left-hand magnet 54,

thence through spring to pins, and thence to the other pole of thebattery 52, which is connected to the metallic bed-plate of theindicator. The left-hand magnet 54, being energized by the current,lifts the left-hand armature-lever 17, allowing the fly t to pass.Immediately after fly t escapes from lever a pin 3 slips off of spring55 by reason of the movement of Wheel P, thereby breaking the circuit ofbattery 52, causing lever 91 to regain its former position and stop flyt after it has made one-half of a revolution. The movement of wheel Pcauses a pin 8 on that wheel to touch spring m, thereby allowing acurrent to flow from binding-post 35 to the bed-plate of the indicator,thence through the bed-plate to pin .9, and thence by spring m and wire3 to magnets 15 of the regulating devices before described. When needle42 returns to pin f, a current flows from battery 52 to magnet y, thenceto spring at, thence to pin 3, which touches said spring from the formermovement of wheel P, and thence through the bed-plate of the indicatorto the other pole of battery 52. Magnet 3 being momentarily energized bythe current, causes fly t to escape, and wheel P to make one-fourth ofarevolution and stop, as before. The circuit through spring m is brokenby this movement of wheel P. If needle 42 touches screw 57, theright-hand magnet 54 is momentarily energized by a current from battery52, as before described, thereby causing wheel P to make one-fourth of arevolution, pin 3 to touch spring m and a current to flow through theright-hand wire 3 to the regulating devices. hen needle 42 returns againto pin f, magnet y is momentarily energized,as before described,byacurrent from battery 52, and wheel P makes one-fourth of a revolutionand stops, as before. The circuit through spring m is broken by thismovement of wheel P. The

advantages of the above-described method are that oxidation is preventedat the contact-points of needle 42, that instruments of fine adjustmentscan be used, and that the .eifect of a jar that would otherwise causesuch an instrument to close and break'the local circuit a great manytimes in quick'succession when needle 42 is very near the point ofcontact is prevented by the circuit being instantly broken by wheel Pafter the first contact of needle The friction of pins 3, rubbingagainst springs m and m is suiii cient to insure electrical contact.Therefore a stronger current from the dynamo or other suitable sourcecan be broken and closed by said means than could be broken and closedby an instrument of line adjustment operating without friction of itscontact-poi nts.

One of the uses of the above method is to operate a combined motor andregulator with economy of power, as described in the fourth section ofthis specification. It is evident that needle 42 can be magneticallydeflected, as in indicator C, before shown, instead of causingdeflection by theexpansion and contraction of wire 50.

If a motor worked by water or compressed air be substituted for electricmotor J of Fig. 9, the pins 5 on wheels P, Fig. 11, may engage with thevalves controlling the fluid working such motors, thereby opening andclosing said valves and operating the motor intermittently for thepurpose before de scribed.

Sixth. Figs. 12 and 13 show methods of controlling the generativecapacity of dynamoelectric machines in accordance with the requirementsof circuits.

Fig. 12 represents a dynamo S5 feeding lamps arranged in series. Thecommutatorbrushes of the dynamo may be attached to shaft 4 of theregulator A in such manner that said brushes are both equally moved byshaft 4 to and from the position for maximum current. If there aretransient irregularities of speed of the engine driving the dynamo, thebrushes are transiently moved to prevent the effect of suchirregularities. If one or more lamps are switched out of circuit, theregulator automatically makes a new adjustment of the brushes, therebyreducing the generative capacity of the dynamo, and consequently thepressure of the current on the lamp-circuit. This adjustment may also bemaintained unaided by the force of the current, as explained in thethird section of this specification. If one or more lamps are added tothe circuit, the brushes are moved and adjusted in the oppositedirection, increasing the generative capacity of the dynamo, also thepressure 'on the lamp-circuit. The new adjustment may be maintained, asbefore stated. By such means the generative capacity of the dynamo iscaused to accord with the requirements of the circuit which it feeds.

Fig. 13 represents a shunt-wound dynamo 86 feeding a circuit withincandescent lamps arranged in multiple arc. The current which isshunted around the field-magnetol' the dynamo passes through therhcostat of the regulator at A, and by this means the magnetic field isincreased or decreased or maintained at a certain degree of strength,thereby causing the output of the dynamo to accord with the requirementsof the circuit which it feeds.

Figs. ll and 15 illustrate another method of preventing wide variancesof currentstrength. In Fig. ll: the small dynamo 92 excites the field ofdynamo 93, which feeds con verter [it at a distance from the dynamo withan alternating current. Both of the dynamos are regulated, as shown bythe drawings, according to the pressure of the current-feeding converter91. The converter 9i feeds two lamp-circuits. Regulators A operate eacha rhcostat, one being included in each lampcircuit to prevent either ofsaid circuits from receiving too much or too little current when theresistance is changed by altering the number of lamps on a circuit.

Storage batteries or converters may be fed with a high-pressure currentfrom a distant dynamo and act at sub-stations from which low-pressurecurrents for lamps are distributed.

Fig. 15 illustrates another mode of dividing a high-pressure currentfrom dynamo 95 into two or more lamp-circuits. The two lamp-circuits atthe right of the figure are separately regulated or compensated by therheostats of regulators A to prevent variances of current in eitherlamp-circuit.

In the above, Figs. 12, 13, 14, and 15, each cnmrent-indicator C iselectrically connected by wires with the circuit to be regulated, andalso by wires 3 and 9 to a regulator A, which controls the circuit, allof which has been explained in detail in the first part of thisspecification.

lVhat I claim is 1. The method of rapidly compensating ineipientvariations of current in a generatoreireuit, which consists in causingtwo or more regulating devices or other compensating agents to actaecuniulativcly each with a progressively-increasing eii'ect the instantthe current varies either byincrease or decrease.

The method of rapidly counteracting incipient variations of current in ageneratorcircnit, which consists in causing two or more regulatingdevices or other compensating agents to actaceumulatively ordifferentially each with a progrcssively-increasing effect the instantcurrent varies either by increase or decrease, thereby preservinguniformity of current.

The method of rapidly counteracting incipient variations of current in ageneratorcircuit, which consists in causing a compensating resistance orcurrent-varying device to act progressively, and neutralizing the effectof an excess of progressive action by causing said compensating deviceto act ditferentially by retrogressive action the instant thecompensation overshoots the required limit.

JULIICN M. BRADFORD.

Witnesses:

II. M. BRADFORD, ALBERT C. NEAL.

